Laminar Flow Control Research Articles

Experiments on Discrete Roughness Element Technology for Swept-Wing Laminar Flow Control

Micrometer-sized spanwise-periodic discrete roughness elements (DREs) were applied to and tested on a 30 deg swept-wing model in order to study their effects on boundary-layer transition in flight in which stationary crossflow vortices were the dominant instability. Significant improvements have been made to previous flight experiments in order to more reliably determine and control the model angle of attack and unit Reynolds number in order to minimize the uncertainties that DREs have on laminar–turbulent transition on a swept wing. Two interchangeable leading-edge surface-roughness configurations were tested: highly polished and painted. The baseline transition location for the painted leading edge (increased surface roughness) was unexpectedly farther aft than the polished. Infrared thermography, coupled with a postprocessing code, was used to globally extract a quantitative boundary-layer transition location. Linear stability guided the DRE configuration test matrix. Although the results have not reliably confirmed the use of DREs as a viable laminar flow control technique in the flight environment, it has become clear that significant computational studies, specifically direct numerical simulation of these particular DRE configurations on this model geometry and flight conditions, are a necessity in order to better understand the influence that DREs have on laminar–turbulent transition

Pharmaceutical Preparations for Intradermal Drug Tests

AbstractOur department of pharmacy takes over all the medical skin tests prescribed by the allergy department. The production takes place in specific premises, with qualified and calibrated equipment, by a qualified and regularly assessed staff—in compliance with the French preparation guidelines. The whole activity is under the responsibility of a pharmacist—handlings are performed by hospital pharmacy technicians. Each new intradermal skin test demand leads to a feasibility analysis—irritating nature, dilution solvent, concentration—this information is gathered in a thesaurus. The manufacturing steps are the following: prescription validation, production sheet and label printing, preparation of the needed equipment, batch numbers and expiration date checking, handling under a vertical laminar flow hood and control after production. The preparation activity increases continuously and the thesaurus currently contents 302 rows with following information: drug, dilution and reconstitution solvent, pure solution concentration and maximum concentration to test with intradermal tests. Work would prospect in costs reduction and resources optimization. Thanks to the allergists’ confidence, the partnership between the two departments can go on. This guarantees the quality of the preparations tested on patients but also the skin tests reproducibility.

Reconfigurable RGB dye lasers based on the laminar flow control in an optofluidic chip.

The optofluidic dye laser serves as an important on-chip optical source in microfluidic technology for a breadth of applications. One of the ultimate goals of such a light source is an optofluidic white dye laser. However, realizing such a device has been challenging, because it is difficult to achieve simultaneous multi-wavelength lasers that span the most visible spectrum, especially on an integrated system. Here, we demonstrate white lasing in an optofluidic chip that simultaneously lases in red, green, and blue (RGB) colors inside a microfluidic channel. A Fabry-Perot cavity formed by two end-coated fibers provides the optical feedback of the laser. Easy reconfigurable emission can be obtained based on the laminar flow control. Eventually, white lasing at a low threshold was obtained when the pumping energy density is in excess of 26.1 μJ/mm2.

Solution rheological parameters modulate calcium phosphate mineralization in a microfluidic device

Mineralization of calcium phosphate and other materials in vivo and in natural water sources occurs in solutions that are not stagnant, but are flowing. Flow conditions could influence solution mixing and, therefore, mineralization kinetics or mechanism. This work describes the design and characterization of a multi-stream parallel flow microfluidic device that allows for controlled solution mixing and indirect control of laminar flow by altering the microfluidic device width, shape, length, flow rate, and flow velocity. Measurement of solution mixing was accomplished using the protonation of quinine to produce a fluorescent molecule and the rate of calcium phosphate mineralization was monitored by optical microscopy and analysis with Image J software. Experiments were designed to hold the flow rate constant, allowing the solution velocity to vary and to hold the velocity constant, allowing the flow rate to vary. It was found that small changes in laminar flow conditions do not correlate to mineral growth, but solution velocity and flow rate have a substantial effect on calcium phosphate mineralization. AFM and SEM characterization of the mineral produced shows an amorphous material and varying degrees of mineralization possibly due to variation in supersaturation conditions across the solution mixing area. This microfluidic device and analysis procedure allows for improved study of mineralization and the effect of flow conditions relevant to those seen in biological settings.

Control of crossflow instability over a swept wing using dielectric-barrier-discharge plasma actuators

This paper investigates the potential use of dielectric-barrier-discharge (DBD) plasma actuators to control the crossflow instability of the boundary layer on a 45° swept NLF-0415 airfoil at −4∘ angle of attack.The disturbance evolution is resolved using nonlinear parabolized stability equations (NPSEs). Actuators are mounted near the leading edge and generate an electric wind perpendicular to the crossflow vortex axes. The spanwise distance between neighboring actuators is first set to be the fundamental wavelength of the unstable mode. This harmonic actuation reduces the disturbance energy only when the induced body force and the disturbance velocity have reverse sign. At certain different locations, the actuators can actually increase the disturbance energy. The robustness in laminar flow control is improved when two actuators per fundamental wavelength are used. This subharmonic actuation leads to reduction in the energy of the primary unstable mode independent of the actuator locations. Finally, the simulation without baseflow forcing reveals that harmonic modes play important roles in this subharmonic control.

Theoretical Modeling and Optimization of Porous Coating for Hypersonic Laminar Flow Control

A theoretical model is developed to describe the acoustic characteristics of plane ultrasonic acoustic waves impinging on a porous coating, namely, a rigid surface periodically corrugated with subwavelength grooves (two-dimensional cavities). The proposed model takes into account the high-order diffracted modes, and therefore incorporates mutual coupling among neighboring cavities. The model predicts a reflection frequency consistent with the numerical results and reproduces a coupling mode induced by interactions between waves scattered from adjacent cavities. With this model, the cavity geometry parameters are optimized to achieve the minimum reflection coefficient. The result shows that the Mack second mode is strongly suppressed and that the maximum fluctuating pressure decreases by about 88% upon using the optimized porous coating in a Mach 6 flat-plate flow.

Control of separated fluid flow and heat transfer characteristics over a backward facing step

ABSTRACTThe control of laminar fluid flow and heat transfer characteristics over a backward facing step have been studied by varying location and orientation of a thin adiabatic fin mounted on the top wall. The detailed investigation of geometrical parameters of fin (length, location and orientation) for two different Reynolds numbers is performed numerically and the results are compared to the case without fin. It is found that fin location and orientation can be used to control the primary reattachment point and the peak of local Nusselt number effectively and it acts as a passive controller.

Cancellation of Tollmien–Schlichting Waves in Direct Vicinity of a Plasma Actuator

The active cancellation of Tollmien–Schlichting waves is a promising and energy-efficient laminar flow control technology with the goal of drag reduction by delaying laminar–turbulent transition. This paper analyzes, for the first time, the control mechanism in the direct vicinity of the actuator using particle image velocimetry. Artificial Tollmien–Schlichting waves are generated at a frequency of in a two-dimensional zero-pressure-gradient flat-plate boundary layer (). The Tollmien–Schlichting waves travel downstream and are attenuated with an unsteady dielectric-barrier-discharge plasma actuator force. Phase-locked particle image velocimetry measurements at an acquisition rate of in double-frame mode are conducted in the direct vicinity of the plasma actuator, resolving 16 phase angles of the wave cycle. The use of two cameras allows measurement of two full wavelengths of the Tollmien–Schlichting waves and a detailed analysis of the cancellation process. The phase-averaged velocity fields of the artificially generated Tollmien–Schlichting waves are validated with a linear stability theory. The wavelength, amplification, and shape of the Tollmien–Schlichting wave disturbances and the counterwaves generated by the plasma actuator are analyzed.

Direct numerical simulation of a compressible boundary-layer flow past an isolated three-dimensional hump in a high-speed subsonic regime

This work was supported by the Laminar Flow Control Centre funded by Airbus/EADS and EPSRC under Grant No. EP/I037946 and computational resources were also provided through the UK Turbulence resource under EPSRC Grant No. EP/L000261/1. The authors would like to acknowledge the use of Imperial College High Performance Computing facility. S.J.S. would also like to acknowledge support under the RAEng Fellowship through Grant No. 10145/86.

A Structural Design Concept for a Multi-Shell Blended Wing Body with Laminar Flow Control

Static and fatigue analyses are presented for a new blended wing body (BWB) fuselage concept considering laminar flow control (LFC) by boundary layer suction in order to reduce the aerodynamic drag. BWB aircraft design concepts profit from a structurally beneficial distribution of lift and weight and allow a better utilization of interior space over conventional layouts. A structurally efficient design concept for the pressurized BWB cabin is a vaulted layout that is, however, aerodynamically disadvantageous. A suitable remedy is a multi-shell design concept with a separate outer skin. The synergetic combination of such a multi-shell BWB fuselage with a LFC via perforation of the outer skin to attain a drag reduction appears promising. In this work, two relevant structural design aspects are considered. First, a numerical model for a ribbed double-shell design of a fuselage segment is analyzed. Second, fatigue aspects of the perforation in the outer skin are investigated. A design making use of controlled fiber orientation is proposed for the perforated skin. The fatigue behavior is compared to perforation methods with conventional fiber topologies and to configurations without perforations.

Drag Reduction by Laminar Flow Control

The Energy System Transition in Aviation research project of the Aeronautics Research Center Niedersachsen (NFL) searches for potentially game-changing technologies to reduce the carbon footprint of aviation by promoting and enabling new propulsion and drag reduction technologies. The greatest potential for aerodynamic drag reduction is seen in laminar flow control by boundary layer suction. While most of the research so far has been on partial laminarization by application of Natural Laminar Flow (NLF) and Hybrid Laminar Flow Control (HLFC) to wings, complete laminarization of wings, tails and fuselages promises much higher gains. The potential drag reduction and suction requirements, including the necessary compressor power, are calculated on component level using a flow solver with viscid/inviscid coupling and a 3D Reynolds-Averaged Navier-Stokes (RANS) solver. The effect on total aircraft drag is estimated for a state-of-the-art mid-range aircraft configuration using preliminary aircraft design methods, showing that total cruise drag can be halved compared to today’s turbulent aircraft.

Laser micro drilling methods for perforation of aircraft suction surfaces

To reduce the fuel consumption of large passenger aircrafts the hybrid laminar flow control is a key technology. For drag reduction, several millions of holes with diameters around 50 µm at the leading edges are needed. In this paper, the perforation of such titanium sheets using the laser processes of single pulse and percussion drilling is presented. The single pulse technique is an “on-the-fly” drilling process using a pulsed fibre laser in combination with a drilling optic with coaxial gas supply. The percussion technique is a flexible drilling process using a q-switched fibre laser combined with a galvanic scanner.

層流制御システムをとりいれた航空機の概念設計手法に基づく性能検討

層流制御システムをとりいれた航空機の概念設計手法に基づく性能検討

10.18178/ijmerr.7.1.1-8

This paper describes a tool developed for estimating performance of suction pumps for Hybrid Laminar Flow Control (HLFC) with constraints related to real aircraft application. The suction pump has three components: a compressor, a generator and a motor. The last two must fit the overall aircraft electric system, which is unknown at this stage. Therefore, general linear approximations are used. The compressor is independent from other systems and is optimized specifically for HLFC. The models have been validated with data from previous HLFC concept studies. The tool, developed in Python, provides sufficient details to ensure the constraints are satisfied, while still requiring minimal computational efforts and allowing the user to choose freely any optimization variables, constraints and objectives functions. This represents the first step toward a system-level optimization of HLFC concepts.

Conditioning of cross-flow instability modes using dielectric barrier discharge plasma actuators

In the current study, selective forcing of cross-flow instability modes evolving on a $45^{\circ }$ swept wing at $Re=2.17\times 10^{6}$ is achieved by means of spanwise-modulated plasma actuators, positioned near the leading edge. In the perspective of laminar flow control, the followed methodology holds on the discrete roughness elements/upstream flow deformation (DRE/UFD) approach, thoroughly investigated by e.g. Saric et al. (AIAA Paper 1998-781, 1998), Malik et al. (J. Fluid Mech., vol. 399, 1999, pp. 85–115) and Wassermann & Kloker (J. Fluid Mech., vol. 456, 2002, pp. 49–84). The possibility of using active devices for UFD provides several advantages over passive means, allowing for a wider range of operating $Re$ numbers and pressure distributions. In the present work, customised alternating current dielectric barrier discharge plasma actuators have been designed, manufactured and characterised. The authority of the actuators in forcing monochromatic stationary cross-flow modes at different spanwise wavelengths is assessed by means of infrared thermography. Moreover, quantitative spatio-temporal measurements of the boundary layer velocity field are performed using time-resolved particle image velocimetry. The results reveal distinct steady and unsteady forcing contributions of the plasma actuator on the boundary layer. It is shown that the actuators introduce unsteady fluctuations in the boundary layer, amplifying at frequencies significantly lower than the actuation frequency. In line with the DRE/UFD strategy, forcing a sub-critical stationary mode, with a shorter wavelength compared to the naturally selected mode, results in less amplified primary vortices and related fluctuations, compared to the critical forcing case. The effect of the forcing on the flow stability is further inspected by combining the measured actuators body force with the numerical solution of the laminar boundary layer and linear stability theory. The simplified methodology yields fast and computationally cheap estimates on the effect of steady forcing (magnitude and direction) on the boundary layer stability.

Specific binding of antigen-antibody in physiological environments: Measurement, force characteristics and analysis

The specific recognition of the antigen by the antibody is the crucial step in immunoassays. Measurement and analysis of the specific recognition, including the ways in which it is influenced by external factors are of paramount significance for the quality of the immunoassays. Using prostate-specific antigen (PSA)/anti-PSA antibody and α-fetoprotein (AFP) /anti-AFP antibody as examples, we have proposed a novel solution for measuring the binding forces between the antigens and their corresponding antibodies in different physiological environments by combining laminar flow control technology and optical tweezers technology. On the basis of the experimental results, the different binding forces of PSA/anti-PSA antibody and AFP/anti-AFP antibody in the same phosphate-buffered saline (PBS) environments are analysed by comparing the affinity constant of the two antibodies and the number of antigenic determinants of the two antigens. In different electrolyte environments, the changes of the binding force of antigens-antibodies are explained by the polyelectrolyte effect and hydrophobic interaction. Furthermore, in different pH environments, the changes of binding forces of antigens-antibodies are attributed to the role of the denaturation of protein. The study aims to recognise the antigen-antibody immune mechanism, thus ensuring further understanding of the biological functions of tumour markers, and it promises to be very useful for the clinical diagnosis of early-stage cancer.

Optimal active control of laminar flow over a circular cylinder using Taguchi and ANN

Increasing the lifetime of engineering structures is dependent on the unsteady forces exerted by vortex shedding. Flow controllers can be used for suppression of vortex shedding behind the cylindrical structures. The main objective of this paper is to minimize the wake generated behind a circular cylinder in laminar flow, Re=150. Two counter rotating controllers inject the momentum in the wake region or actively control the vortex shedding. The important parameters for defining the effectiveness of flow control are the lift and drag fluctuations besides the drag coefficient. The computational methodology is based on the finite volume method using the SIMPLE algorithm. The parameters that affect on the wake control are the rotation rate, diameter of controllers, radial and the angular distances. Determining the optimum governing parameters is important. A neural network is used for finding these optimum parameters. The input data for training this neural network were provided by the Taguchi method. Moreover the Taguchi method clarified the influence of each parameter on the wake generation. At the optimal obtained conditions the drag coefficient reduced up to 99.99% and the vortex shedding suppressed appropriately.

Cross-flow effects regarding laminar flow control within conceptual aircraft design

PurposeLaminarization of commercial aircraft surfaces is the most promising technology to reduce fuel consumption and ecological impact. As laminar flow highly depends on cross-flow effects, there is the question in which way simple estimations and simplifications for application in conceptual aircraft design can be used to capture these cross-flow influences. This paper aims to show the accuracy of 2D methods for estimating laminar flow regions on 3D wing objects.Design/methodology/approachSeveral methods, relating 3D and 2D flow conditions, are analyzed with regard to capture cross-flow influences. The 3D pressure distributions depending on utilized transformation method are compared to Reynolds-averaged Navier–Stokes (RANS) solutions. With the most precise transformation method, the laminar flow area on a conventional wing of a short range aircraft is determined and compared to the laminar area obtained with the RANS pressure distributions as input. Further, hybrid laminar flow control component sizing is carried out to obtain the net benefit in fuel reduction of simplified method compared to RANS method for a conventional short range aircraft.FindingsIn this particular case, the solutions calculated with the simplified methods show high deviations from those obtained with RANS.Originality/valueThis investigation underlines the need of proper methods for fast and accurate estimation of cross-flow effects to be able to assess the full potential of laminar flow control within conceptual aircraft design.

Organic electrosynthesis in flow microreactor

Recently, microreactor technology has received significant research interest from both academia and industry. Fundamental advantages and potential benefits of microreactor technology are an extremely large surface-to-volume ratio, precise temperature control, precise residence time control, strict laminar flow control, extremely fast molecular diffusion, and improvement of reaction process safety. These advantages and benefits can be applied to a wide range of organic synthesis and organic mass production processes. Electron transfer is one of the most common driving factors for organic reactions, and organic electrosynthesis serves as a straightforward and powerful method of organic electron-transfer processes. The integrated use of microreactor technology with organic electrosynthesis is one of the most sophisticated processes in organic chemistry. In addition, novel systems that are realized only by using electrochemical microflow reactors have been developed recently. This review summarizes recent advances in organic electrosynthesis using flow microreactors.

Comparison of the effects of surface roughness and confinement on rotor–stator cavity flow

ABSTRACTResults of a computational study are discussed which investigate roughness-induced and geometry-induced (confinement) effects on the steady-state velocity components in 3-D boundary-layer flow over the rotor disc in a rotor–stator flow configuration. It is found that, for the rotor–stator flow investigated, the roughness-induced effects are very similar to geometry-induced effects, both in nature and magnitude. The overall aim was to compare these two types of effects with corresponding roughness-induced effects in the von Kármán boundary-layer flow over a disc spinning freely in an unrestricted fluid environment. The research was conducted in the context of a programme investigating surface roughness as a means of laminar flow control for the development of new passive drag-reduction techniques. The goal was to establish whether it was possible unequivocally to distinguish between roughness-induced and geometry-induced effects on the boundary-layer flow above the rotor disc. The results obtained suggest that, for the type of system discussed here, it must be expected to be difficult to distinguish between these effects in experiments. The similarities regarding the nature and magnitude of results obtained from comparing predictions for three different computational modelling approaches indicate the required sensitivity of measurement technologies aiming to resolve the investigated effects in experimental studies.